docs(showcase): add "Live Metadata Views" example doc (ADR-0051 P1) (#1951)

A `doc` whose Markdown embeds four ```metadata fences — two state
machines (task/project lifecycles), a flow at business altitude, and a
permission matrix — demonstrating ADR-0051 inline metadata views.

Compiles via the existing doc collector (the fence is valid CommonMark,
not MDX); renders live once the objectui `element:metadata_viewer`
(objectstack-ai/objectui#1774) is deployed. Verified end-to-end in the
browser against this showcase backend.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: os-zhuang

examples/app-showcase/src/docs/showcase_metadata_views_guide.md

@@ -0,0 +1,64 @@
+---
+title: Live Metadata Views in Docs
+description: Embed live, read-only views of state machines, flows, and permissions directly in the prose.
+---
+
+# Live Metadata Views in Docs
+
+Documentation is for the reader who can't — or shouldn't — open Studio: a
+business analyst, a project manager, an auditor. For them a running screen only
+ever shows *their own slice* of the system. It never shows the whole shape of a
+process, the full set of legal state transitions, or who can do what across an
+object.
+
+This page embeds those **live, read-only views** straight into the prose with a
+` ```metadata ` fenced block. Each view is **resolved at read time** from the
+current metadata — change the underlying state machine and the diagram below
+changes with it. Nothing here is a screenshot (ADR-0051).
+
+## A record lifecycle — state machine
+
+A Task moves across a board. Which moves are legal is governed by the
+`task_status_flow` state machine on the `showcase_task` object. Here it is,
+rendered live from that rule:
+
+```metadata
+type: state_machine
+object: showcase_task
+name: task_status_flow
+```
+
+Projects have their own lifecycle, including terminal (dead-end) states:
+
+```metadata
+type: state_machine
+object: showcase_project
+name: project_status_flow
+```
+
+## A process — flow
+
+The reassignment wizard, shown at the **business altitude** — purely technical
+steps (scripts, record I/O) are folded away so the reader sees the process, not
+the plumbing:
+
+```metadata
+type: flow
+name: showcase_reassign_wizard
+detail: business
+```
+
+## Who can do what — permission
+
+The `showcase_contributor` permission set, as an object-access matrix:
+
+```metadata
+type: permission
+name: showcase_contributor
+```
+
+---
+
+> These four views are not authored prose — they are the live metadata,
+> projected read-only into the document. See
+> [the showcase overview](./showcase_index.md) for the rest of the workspace.